1. Field of the Invention
The present invention generally relates to integrated circuits and, more specifically to a complementary transistor structure having a Mott material oxide channels.
2. Description of the Related Art
Silicon based metal oxide semiconductor field effect transistors (MOSFETs) are reaching the limits of scaling (e.g., reduction in size) due to, among other things, doping and double depletion effects. In other words, as semiconductor devices are reduced in size, the depletion regions are placed in closer proximity to one another. This often results in merging or shorting of the adjacent depletion regions.
Silicon MOSFET technology is expected to scale to 0.1 micron channel length devices after the year 2000. Below 0.1 microns however, there are fundamental physical effects which can limit silicon MOSFET technology, including: short channel effects, dopant number fluctuations, ballistic transport and tunneling through thin gate oxides. These effects may limit the minimum channel length in silicon MOSFET technology to an estimated 30 nm.
One solution to the scaling problem is a field effect transistor (FET) formed with a channel oxide capable of undergoing a metal-insulator transition known as a Mott transition (e.g., a Mott FET or MTFET).
A Mott FET is a solid state switching device made of oxide materials and is discussed in more detailed in Mott Transition Field Effect Transistor, Applied Physics Letters, Vol 73, Number 6, pages 780-782, Aug. 10, 1998, incorporated herein by reference. The Mott FET device includes a channel connecting source and drain electrodes, a gate oxide and a gate electrode.
For example, a Mott FET device is shown in FIG. 13. The device includes a conductive substrate 1301 (e.g., Nb-STO (100)-cut crystal) which forms the gate electrode, a gate oxide layer 1300 (e.g., strontium titanate (STO)) epitaxially grown on the substrate 1301, a Mott conductor-insulator transition channel 1302 (e.g., epitaxially grown cuprate material such as Y1xe2x88x92xPrxBa2CU3O7xe2x88x92xcex4(YPBCO, LCO)), source and drain electrodes 1303 and an isolation trench 1304. With the structure shown in FIG. 13, when an electric field is applied to the gate 1300, the channel 1302 changes from an insulator to a conductor (or vice versa) to make or break a connection between the source and drain 1303.
The Mott FET device is quite distinct from conventional silicon metal oxide field effect transistors in that the channel is a Mott insulator, a material with a characteristic, controllable, conductor-insulator transition, used in place of a semiconductor. A Mott FET device offers significant potential for scaling to the nanometer dimensions for integration with ferroelectric materials in non-volatile storage roles and for fabrication of multilayer device structures. Mott FET devices remain adequate on a nanoscopic scale which is well beyond the current projected limits of silicon MOSFET scaling.
However, the Mott FET discussed above has a number of limitations. Specifically, the structure shown in FIG. 13 results in the channel layer 1302 being exposed to subsequent processing steps, which may damage or undesirably change the channel layer 1302. Also, conventional Mott-FET devices suffer from the shortcoming that the channel layer is not protected. Further, they have a common gate electrode which does not allow the formation of a complementary cell.
It is, therefore, an object of the present invention to provide a structure and method for manufacturing a complementary field effect transistor structure that includes forming a first type Mott channel layer and forming a second type Mott channel layer adjacent the first type Mott channel layer, wherein the first type Mott channel layer is complementary to the second type Mott channel layer.
The method may also include forming a first source region, a first drain region and a first gate conductor region adjacent the first type Mott channel layer and forming a second source region, a second drain region and a second gate conductor region adjacent the second type Mott channel layer. The first source region, the first drain region, the first gate conductor region and the first Mott channel layer are a first type field effect transistor and the second source region, the second drain region, the second gate conductor region and the second type Mott channel layer are a second type field effect transistor electrically connected to the first type field effect transistor.
The forming of the first source region and the first drain region includes forming a first conductive layer adjacent the first type Mott channel layer and forming a first insulator region in the first conductive layer opposite the first gate conductor. The first source region and the first drain region are regions in the first conductive layer on opposite sides of the first insulator region.
Similarly, the forming of the second source region and the second drain region includes forming a second conductive layer adjacent the second type Mott channel layer and forming a second insulator region in the second conductive layer opposite the second gate conductor. The second source region and the second drain region are regions in the second conductive layer on opposite sides of the second insulator region.
Also, the forming of the first gate conductor region and the forming of the second gate conductor region include forming a gate conductor layer insulated from and positioned between the first type Mott channel layer and the second type Mott channel layer (the first conductive layer and the second conductive layer respectively being on opposite sides of the first type Mott channel layer and the second type Mott channel layer from the gate conductor layer) and forming a plurality of insulator regions in the gate conductor layer. The first gate conductor region is a region of the gate conductor layer between two of the insulator regions and is positioned opposite and between the first source region and the first drain region. Similarly, the second gate conductor region is a region of the gate conductor layer between two of the insulator regions and is positioned opposite and between the second source region and the second drain region.
The method may also include forming a first conductive oxide layer as the first conductive layer, forming the first type Mott transition layer on the first conductive oxide layer, forming a first gate insulator layer on the first type Mott channel layer, forming a second conductive oxide layer as the gate conductor layer on the first gate insulator layer, forming a second gate insulator layer on the second conductive oxide layer, forming the second type Mott channel layer on the second gate insulator layer and forming a third conductive oxide layer as the second conductive layer on the second type Mott channel layer.
The first type Mott channel layer and the second type Mott channel layer change conductivity in the presence of an electric field. The first type field effect transistor and the second type field effect transistor can be connected to form a complementary field effect transistor.
Another inventive method of manufacturing a complementary field effect transistor structure includes forming a laminated structure having a first side and a second side (the first side including a first type Mott channel layer and the second side including a second type Mott channel layer), forming a first source region and a first drain region in a first conductive layer on the first side, forming a second source region and a second drain region in a second conductive layer on the second side and forming a first gate conductor region and a second gate conductor region in a gate conductor layer positioned between and insulated from the first type Mott channel layer and the second type Mott channel layer. The first source region, the first drain region, the first gate conductor region and the first type Mott channel layer make a first type field effect transistor and the second source region, the second drain region, the second gate conductor region and the second type Mott channel layer make a second type field effect transistor.
Another embodiment of the invention is a method of manufacturing a complementary field effect transistor structure that includes forming a first type Mott channel layer over a first portion of a substrate and forming a second type Mott channel layer over a second portion of the substrate. The first type Mott channel layer is complementary to the second type Mott channel layer.
Further, the invention includes a method of manufacturing a complementary field effect transistor that includes forming a release layer on a substrate, removing a first portion of the release layer to expose a first portion of the substrate and to allow a second portion of the release layer to remain, forming a first portion of a first type Mott channel layer over the first portion of the substrate and a second portion of the first type Mott channel layer over the second portion of the release layer, forming a first portion of a first insulator layer over the first portion of the first type Mott channel layer and a second portion of the first insulator layer over the second portion of the first type Mott channel layer, removing the second portion of the release layer to, release the second portion of the Mott channel layer and the second portion of the first insulator layer and to expose the second portion of the substrate, forming a first portion of a second type Mott channel layer over the first portion of the first insulator layer and forming a second portion of the second type Mott channel layer over the second portion of the substrate, forming a first portion of a second insulator layer over the first portion of the second type Mott channel layer and a second portion of the second insulator layer over the second portion of the second type Mott channel layer and removing the first portion of the second insulator and the first portion of the second type Mott channel layer.
Before the second portion of the release layer is removed a via is formed between: the first portion of the first insulator and the first portion of the first type Mott channel layer; and the second portion of the first insulator, the second portion of the first type Mott channel layer and the second portion of the release layer. The removing of the first portion of the second insulator and the first portion of the second type Mott channel layer includes one of, dry lithographic patterned etching, wet lithographic patterned etching and chemical mechanical polishing.
The complementary field effect structure according to the invention includes a first type Mott channel layer and a second type Mott channel layer adjacent the first type Mott channel layer. The first type Mott channel layer is complementary to the second type Mott channel layer.
The structure also includes a first source region, a first drain region and a first gate conductor region adjacent the first type Mott channel layer and a second source region, a second drain region and a second gate conductor region adjacent the second type Mott channel layer. The first source region, the first drain region, the first gate conductor region and the first Mott channel layer make a first type field effect transistor. The second source region, the second drain region, the second gate conductor region and the second type Mott channel layer make a second type field effect transistor electrically connected to the first type field effect transistor.
The first source region and the first drain region may include a first conductive layer adjacent the first type Mott channel layer and a first insulator region in the first conductive layer opposite the first gate conductor. The first source region and the first drain region being regions in the first conductive layer on opposite sides of the first insulator region.
Similarly, the second source region and the second drain region may include a second conductive layer adjacent the second type Mott channel layer and a second insulator region in the second conductive layer opposite the second gate conductor. The second source region and the second drain region are regions in the second conductive layer on opposite sides of the second insulator region.
Also, the first gate conductor region and the second gate conductor region may include a gate conductor layer insulated from and positioned between the first type Mott channel layer and the second type Mott channel layer (the first conductive layer and the second conductive layer respectively being on opposite sides of the first type Mott channel layer and the second type Mott channel layer from the gate conductor layer) and a plurality of insulator regions in the gate conductor layer. The first gate conductor region being a region of the gate conductor layer between two of the insulator regions and positioned opposite and between the first source region and the first drain region. The second gate conductor region being a region of the gate conductor layer between two of the insulator regions and positioned opposite and between the second source region and the second drain region.
The first conductive layer, the second conductive layer and the gate conductor layer are conductive oxide layers, and the first type Mott transition layer is positioned on the first conductive layer. The structure also includes a first gate insulator layer positioned on the first type Mott channel layer (the gate conductor layer being positioned on the first gate insulator layer) and a second gate insulator layer positioned on the gate conductor layer (the second type Mott channel layer being positioned on the second gate insulator layer and the second conductive layer being positioned on the second type Mott channel layer).
The first type Mott channel layer and the second type Mott channel layer change conductivity in the presence of an electric field. The first type field effect transistor and the second type field effect transistor can be connected to form a complementary field effect transistor.
Another embodiment of the invention is a complementary field effect transistor structure that includes a laminated structure having a first side and a second side (the first side including a first type Mott channel layer and the second side including a second type Mott channel layer), a first conductive layer on the first side having a first source region and a first drain region, a second conductive layer on the second side having a second source region and a second drain region and a gate conductor layer positioned between and insulated from the first type Mott channel layer and the second type Mott channel layer (the gate conductor layer having a first gate conductor region and a second gate conductor region). The first source region, the first drain region, the first gate conductor region and the first type Mott channel layer form a first type field effect transistor and the second source region, the second drain region, the second gate conductor region and the second type Mott channel layer form a second type field effect transistor.
A further embodiment of the invention is a complementary field effect transistor structure that includes a substrate having first and second portions, a first type Mott channel layer positioned over the first portion of the substrate and a second type Mott channel layer positioned over a second portion of the substrate. The first type Mott channel layer is complementary to the second type Mott channel layer.
The invention overcomes the problems associated with conventional semiconductor structures by utilizing the laminated structures shown in FIGS. 1 and 9 to create complementary metal oxide field effect transistor devices which do not include doped diffusion regions and which, therefore, can be made much smaller than conventional semiconductor devices.